1. Field of the Invention
The present invention relates generally to a method of, and apparatus for, folding the edges of a sheet of material, and more particularly, is concerned with a method of, and apparatus for, simultaneously folding several edges of pre-formed plastic blisters, such as those commonly used as a cover in the "blister" package form of packaging.
2. Description of the Prior Art
Although the present invention is suited for folding the edges of any type of material which is either flexible or which is rigid and will yield when heat is applied to the material in a localized area, it is particularly suited to folding the edges of the transparent plastic sheets which are used for the covers of blister-type packages on which it is desired to leave a flat unfolded flange portion.
A frequently used type of packaging currently found in retail stores is the transparent blister package. Blister packages are most often used in the case of goods in which it is desirable for the customer to view and, in many cases, examine the article(s) to be purchased outside of the package without destroying the entire package. In the typical blister package, the articles are placed on a flat piece of backing and are then covered with a transparent plastic material.
Numerous types of blister packages are currently in use. In one version of the blister package, the articles are placed on the backing and are sealed to the backing by a heat sealable transparent plastic material. In some cases this type of blister package is desirable because of its unitary sealed character. In other cases, however, it is desirable to provide a package which can be opened without destroying the package itself in order to inspect the articles inside. In these latter cases, a slidable blister package has been used. In the case of a slidable blister package, instead of being sealed to the backing, the plastic sheet is folded on the edges and on the bottom, and the backing slides in between the edges of the plastic sheet and is retained at the bottom.
The present invention is concerned with a method and apparatus for folding the edges of what will be referred to as a "pre-formed blister" which is intended to describe the sheets of plastic used in the slidable version of the blister package on which a concave portion for holding the articles to be displayed has already been formed, but which has not yet been folded at the edges to make it adaptable for receiving the cardboard backing.
Methods and apparatus are available for simultaneously folding the edges of flexible sheets of plastic and other types of flexible materials, provided that the material to be folded does not have any significant contours on its surface. There appears, however, to be a lack of a suitable method and apparatus for simultaneously folding the edges of a material which is rigid, and which has a substantial contour in the surface thereof, such as those materials commonly used to form the cover of a slidable-type blister package.
The means which are used for folding the edges of the transparent pre-formed blister used in the slidable version of the blister package are seen in Allen U.S. Pat. No. 3,978,191 and Taber U.S. Pat. No. 2,487,494. The process and apparatus shown in the Allen patent folds two parallel edges of a sheet-like material by passing the sheet-like material through a series of rollers on each side of the material which are tilted at gradually increasing angles to form the folds on the edges. This process and apparatus suffers the drawback that it is not capable of folding the bottom edge of the plastic sheet simultaneously with the side edges. As a result, the plastic sheet must be removed from the apparatus and passed through a separate machine which folds the bottom. Because a greater number of steps are involved, this has the effect of increasing the cost of making the blister package as well as the time in which each package can be produced.
The Taber method of folding plastic sheet material operates by positioning a piece of plastic over a gap between two fold forming bars, then contacting the plastic sheet with a heated bar in order to bend the same down into the space between the two fold forming bars, and then clamping the sheet together with the movement of the clamping bars. The Taber method suffers the limitation that it is only capable of folding a single edge of a sheet of plastic in one operation.
Other inventions, such as those disclosed in U.S. Pat. Nos. 4,239,572, 4,019,944, 3,147,172, and their cross references, have not been known to have been used to fold the edges of pre-formed blisters used in blister packaging. In addition to being a great deal more complicated than the instant invention, they provide no means for folding the rigid type of plastic used for the covers in blister-type packaging, or for folding plastic articles having any type of contour in their surface and leaving an unfolded flat flange around the contour, or for leaving a space between the folded edge and the unfolded flange needed to receive the cardboard backing in order to form a completed blister package.
Consequently, a need exists for a process and apparatus for simultaneously folding the edges of a pre-formed plastic blister which is simple to manufacture and use, and which adequately overcomes the deficiencies of the prior attempts to satisfy this need.